1. Technical Field
This patent application relates, in general, to suppressing electromagnetic radiation in and around data processing systems.
2. Description of the Related Art
Data processing systems generally include electronic components (e.g., integrated circuits, resistors, capacitors, etc.) which are typically mounted on or integrated within printed circuit boards. A printed circuit board is a board made of non-conducting material, such as plastic, glass, ceramic, or some other dielectric on which electronic components are mounted. A printed circuit board has metallic tracings to provide electrical connections between various electronic components mounted on the printed circuit board.
During operation of a data processing system, one or more electronic components typically send electronic signals over one or more conductive paths (e.g., metallic traces) of one or more printed circuit boards. Such electronic signals often result in electromagnetic energy being radiated.
Electromagnetic radiation can interfere with data processing system operation (in which case the electromagnetic radiation is referred to as electromagnetic interference (EMI)). Accordingly, efforts are made within the art to suppress electromagnetic radiation emission from and around printed circuit boards and/or their associated electronic components.
One way in which electromagnetic radiation emissions are conventionally suppressed is via the use of what is known in the art as Low Voltage Differential Signaling (LVDS). LVDS is illustrated in FIG. 1.
With reference now to FIG. 1, shown is a partially schematic diagram depicting an example of LVDS via use of differential driver 100 which is contained within one or more printed circuit board 550. Illustrated is that differential driver 100 produces first voltage waveform 102, shown for sake of example as a square wave ranging between 0 and +5 volts which typically would have a period of around 2 nano-seconds (e.g., a 500 MHz waveform, very commonly used in microprocessor systems, has a period of 2xc3x9710xe2x88x929 seconds), on first printed-circuit-board trace 104. Also shown is that second voltage waveform 106, which is depicted as an exact inverse of first voltage waveform 102, and which is illustrated for sake of example as a square wave ranging between 0 and xe2x88x925 volts which also typically would have a period of around 2 nano-seconds (e.g., the period of a 500 MHz waveform), on second printed-circuit-board trace 108, which is the exact inverse of first voltage waveform 102 in voltage and which is exactly synchronized with first voltage waveform 102 in time.
There are at least two intents involved in LVDS. A first intent is to increase the accuracy of any data processing system in which LVDS is used, since the difference of the received signal will give a signal of twice the magnitude of either of the differential signals taken alone. For example, if second waveform 106 is subtracted from first waveform 102, resultant signal will be a square wave waveform of twice the magnitude of first voltage waveform 102.
A second intent of LVDS is to reduce the amount of electromagnetic energy radiated by voltage waveform 102 and voltage waveform 106. This is illustrated by resultant radiated energy graph 110. The intent of resultant radiated energy graph 110 is to show that at some distance from printed-circuit-board traces 104 and 108, the energies respectively radiated by voltage waveform 102 and 106 substantially cancel each other. While those skilled in art will recognize that the energies do not typically cancel to exactly zero as indicated by resultant radiated energy graph 110, those skilled in the art will appreciate that the cancellation LVDS does tend to be substantially effective.
There are certain instances, described below, in which the differential signals, or waveforms, used in LVDS get out of phase (i.e., become un-synchronized in time). Such a lack of synchronization can create radiated energy in a fashion such as that illustrated in FIG. 2.
Referring now to FIG. 2, depicted is differential driver 200, substantially analogous to differential driver 100, in which second waveform 206, output by differential driver 200 on first printed-circuit-board trace 208, is slightly out of phase (or time synchronization) with first waveform 202 output by differential driver 200 on second printed-circuit-board trace 204. Illustrated by resultant radiated energy graph 210 is that at some distance from printed-circuit-board traces 204 and 208 substantial energy is radiated by voltage waveform 202 and 206, in that the phase-mismatch, or time slipping, of one waveform in relation to the other indicates that they do not cancel each other.
There are numerous ways that initially time-synchronized LVDS signals can become un-synchronized (i.e., develop a phase differential) when traveling within separate printed-circuit-board traces. One example showing how initially time-synchronized LVDS signals can become un-synchronized is illustrated in FIG. 3.
With reference now to FIG. 3, illustrated is an example of how LVDS can get out of phase. Shown is differential driver 100 driving first and second printed circuit traces 300 and 302. Depicted are that printed circuit traces 300 and 302 are formed in circular arc fashion, about a point P, with a xe2x80x9cradius,xe2x80x9d R1, of about 2 units for inner trace 302 and a xe2x80x9cradius,xe2x80x9d R2, of about 3 units for outer trace 300, with the arc of printed circuit trace 302 arranged inside that of the arc of printed circuit trace 300. Here, theta, in radians is roughly xcfx80/2. Those skilled in the art will recognize that the formula for circular arc length is approximately R*xcex8. Thus, the distance traveled by a signal on inner trace 302 is about xcfx80/2 units less than that traveled by a signal on outer trace 300. Consequently, insofar as that the electrical energy in both inner trace 302 and outer trace 300 travels at about the same velocity, signal 102 traveling on outer trace 300 will arrive at the endpoint of outer trace 300 time-delayed relative to signal 104 (initially time-synchronized with signal 102) traveling on inner trace 302. To illustrate this, shown in FIG. 1 is a sample calculation with units set to inches. The units are expressed in inches for ease of illustration, but those skilled in the art will recognize that in typical printed circuit boards, units of length are usually expressed in terms of xe2x80x9cmilsxe2x80x9d (standing for thousandths of an inch). The calculation used in FIG. 3 essentially states that a distance, d, traveled by a point on an electromagnetic energy waveform (e.g., a point on a square wave) multiplied by (1/(velocity of the electromagnetic energy waveform in a particular medium)) equals the time it takes for the point on the electromagnetic waveform to traverse the distance d. Illustrated is that the different-length paths followed by inner trace 302 and outer trace 304 result in loss of time synchronization between signal 102 and 104, which will accordingly give rise to electromagnetic energy radiation analogous to that described in relation to FIG. 2.
In printed circuit board layout design, it is not uncommon for printed-circuit-board traces carrying paired LVDS signals to take slightly different paths, such as those illustrated in relation to FIG. 3 (albeit on a much smaller scale), along and through a printed circuit board. Such varying paths which quite often result in a phase difference between respectively paired LVDS waveforms. This fact has long been recognized, and it is conventional within the art to build in some architecture at the end of the trace taking the shorter path on and/or through the printed circuit board in order to delay the signal on the shorter path such that the signal on the longer path has a chance to xe2x80x9ccatch upxe2x80x9d with the signal on the shorter path, thereby allowing the LVDS signals to be xe2x80x9cdifferencedxe2x80x9d to achieve one of the intended benefits of LVDS signaling. Examples of printed-circuit-board traces employing this technique are illustrated in FIG. 4.
Referring now to FIG. 4, shown are printed-circuit-board traces wherein the conventional approach of inserting a delay near the end of a printed-circuit-board trace to make up for different lengths traversed by LVDS signal is illustrated. Shown are printed-circuit-board trace pairs 402, 404, 406, and 408, where various implementations of the conventional technique are shown. With respect to printed-circuit-board trace pair 402, shown is lengthening trace segment 412, which delays the signal on printed-circuit-board trace 422 relative to the signal on printed-circuit-board trace 432, hopefully such that the signal on printed-circuit-board trace 422 and the signal on printed-circuit-board trace 432 can be brought back into time synchronization prior circuit termination point 460. Likewise shown are lengthening trace segments 414, 416, and 418 which respectively function for printed-circuit-board trace pairs 404, 406, and 408 in a fashion substantially analogous to that described for lengthening trace segments 414, 416, and 418. For example, lengthening trace segment 414 delays the signal on printed-circuit-board trace 424 relative to the signal on printed-circuit-board trace 434, lengthening trace segment 416 delays the signal on printed-circuit-board trace 426 relative to the signal on printed-circuit-board trace 436, and lengthening trace segment 418 delays the signal on printed-circuit-board trace 428 relative to the signal on printed-circuit-board trace 438.
It has been discovered by the inventors named herein that while conventional lengthening trace segments such as lengthening trace segments 412, 414, 416, and 418 can and do bring out-of-phase signals back into phase prior to delivery of the signals to the endpoint of printed-circuit-board traces, the use of such conventional lengthening trace segments allows significant radiated energy emissions to arise as signals on each trace making up a printed-circuit-board trace pair transit each trace prior to encountering the conventional lengthening trace segments. In addition, the inventors named herein have also discovered that conventional lengthening trace segments such as lengthening trace segments 412, 414, 416, and 418 also cause excessively high impedance.
In light of the foregoing-noted discoveries of the inventors named herein, it is apparent that a need exists for a method and system which will decrease the amount of radiated emissions and excessive impedance associated with the use of conventional lengthening trace segments, such as lengthening trace segments 412, 414, 416, and 418, to re-synchronize LVDS signals which have become un-synchronized.
Although the preceding discussion has referred to LVDS for ease of illustration, those having skill in the art will recognize that the foregoing discussion applies generally to virtually all types of xe2x80x9cdifferential signaling,xe2x80x9d of which LVDS is merely one type. Examples of other types of differential signaling include but are not limited to the following: USB (Universal Serial Bus) signaling, IEEE-1394 signaling, Ethernet signaling, RS-422 signaling, RS-485 signaling, AGP (Accelerated Graphics Port) 4xc3x97 signaling, and ECL (Emitter Coupled Logic) signaling. Accordingly, the remainder of the present application makes reference to xe2x80x9cdifferential signalingxe2x80x9d which is intended to be indicative of at least substantially all of the foregoing recited types of differential signaling.
The inventors named herein have discovered a system and method which decrease the amount of radiated emissions and excessive impedance associated with the use of conventional methods and systems to re-synchronize signals which have become un-synchronized. Advantages of the system and method are described in more detail in the detailed description, below.
In one embodiment, the system includes but is not limited to a section of a first printed-circuit-board conductive element, the section of the first printed-circuit-board conductive element formed to follow at least one bent segment of a first printed-circuit-board path; a section of a second printed-circuit-board conductive element, the section of the second printed-circuit-board conductive element having at least a first part formed to follow at least one bent segment of a second printed-circuit-board path, where the at least one bent segment of the second printed-circuit-board path is substantially proximate to and has a length less than a length of the at least one bent segment of the first printed-circuit-board path; and the section of the second printed-circuit-board conductive element having at least a second part formed to follow a conductive-section-equalization feature which deviates from the second printed-circuit-board path, the at least a second part situated substantially proximate to the at least one bent segment of the second printed-circuit-board path and of length sufficient to make a length of the section of the second printed-circuit-board conductive element substantially the same as a length of the section of the first printed-circuit-board conductive element.
In one embodiment, a related method for manufacturing includes but is not limited to forming a section of a first printed-circuit-board conductive element to follow at least one bent segment of a first printed-circuit-board path; forming a section of a second printed-circuit-board conductive element to have at least a first part shaped to follow at least one bent segment of a second printed-circuit-board path, where the at least one bent segment of the second printed-circuit-board path is substantially proximate to and has a length less than a length of the at least one bent segment of the first printed-circuit-board path; and forming the section of the second printed-circuit-board conductive element to have at least a second part shaped to follow a conductive-section-equalization feature which deviates from the second printed-circuit-board path, the at least a second part situated substantially proximate to the at least one bent segment of the second printed-circuit-board path and of length sufficient to make a length of the section of the second printed-circuit-board conductive element substantially the same as a length of the section of the first printed-circuit-board conductive element.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of this patent application will become apparent in the non-limiting detailed description set forth below.